It is generally known for a cellular wireless communication device (WCD) to engage in voice calls via a cellular radio access network (RAN). A traditional RAN includes one or more mobile switching centers (MSCs), each of which is connected with one or more base station controllers (BSCs), and each BSC is in turn connected with one or more base transceiver stations (BTSs) that define cellular wireless coverage areas in which wireless communication devices can operate.
Typically, each BTS includes an antenna tower with antennas arranged to radiate in a desired pattern so as to produce a desired level of coverage, defining a cell and a number of cell sectors. Each BSC then functions to manage air interface communications, such as to assign air interface traffic channels over which WCDs can communicate, and to manage handoff of communications as a WCD moves between coverage areas (e.g., sectors). Each MSC, in turn, functions as a switching point, to provide connectivity between various WCDs in its coverage, and between WCDs and the public switched telephone network, and further to facilitate handoff of communications as a WCD moves between BSC serving areas or MSC serving areas.
Conventionally, each WCD has an assigned identifier, such as a mobile identification number (MIN) or mobile directory number (MDN), that the RAN may use to identify and track the WCD.
When a WCD powers on in, or otherwise enters, a coverage area (such as an area served by a particular BTS, BSC, or MSC), the WCD may register with the RAN, so the RAN can know where the WCD is located (e.g., for purposes of directing calls to the WCD) and so the RAN can verify that the WCD is authorized to engage in wireless communications. In a typical radio network registration process, the WCD sends a radio access registration message over the air to the RAN via an access channel and, assuming a successful registration, the RAN then sends a radio access registration acknowledgment message to the WCD via a paging channel.
For example, in a system compliant with the well known CDMA (e.g., CDMA2000®) and IS-41 protocols, a WCD engages in radio network registration by sending over the air (via the access channel) to the BTS and, in turn to the BSC, an “access probe,” which carries an identifier of the WCD (such as its MIN or MDN) and other pertinent information. When the BSC receives the access probe, the BSC passes the access probe along to the MSC, and the MSC then sends an IS-41 “Registration Notification” message to a home location register (HLR).
The HLR stores a service profile for each WCD that is authorized to operate in the RAN. Each MSC is coupled with an HLR, typically by an out of band signaling network. Besides authorizing service, the HLR service profile may also be used to store and thereby track location information reflecting a current location in a wireless service provider's network of each authorized WCD.
When a registration notification message is received by the HLR, the HLR updates the WCD's profile to indicate where the WCD is operating (e.g., which MSC is serving the WCD) and may further carry out an authentication process. The HLR may then send an IS-41 registration notification return result, typically including the WCD's service profile, to the corresponding serving MSC. The serving MSC may then store the profile in a local visitor location register (VLR) and send a registration acknowledgement over the air (in an air interface paging channel) to the WCD to complete the registration process.
In order to avoid a buildup of profiles at the MSC, WCDs served by the RAN may be required to re-register with the RAN at a re-registration interval. The re-registration interval may be used to determine whether WCDs currently being served by the RAN have either left the service area of the RAN or have powered off. Once a RAN establishes a re-registration interval and informs WCDs operating within its service area of the interval, it may unload profiles of WCDs that fail to re-register within that interval. For example, if a re-registration interval assigned to a particular WCD passes without the WCD sending a re-registration request, the MSC may assume that the WCD has left the service area or powered-off, and the MSC may unload the profile associated with the WCD, thereby freeing resources in the RAN to serve new WCDs that have entered the service area or powered on.
The RAN may notify each WCD it is serving of an assigned re-registration interval by including the assigned re-registration interval within a registration acknowledgment message or in a separate message. For example, a re-registration interval message solely directed to transmitting the assigned re-registration interval to the WCD could be sent at some point after sending the registration acknowledgment message. In the latter case, the re-registration interval may be measured either from receipt of the initial registration acknowledgment message or from receipt of the re-registration interval message.
The re-registration interval assigned to WCDs operating within the service area of the RAN may be fixed and may be determined by an operator of the RAN, or may vary dependent upon other variables, such as system load or time of day. For example, the re-registration interval may be twenty minutes during the day and forty minutes during the night. In such a case, and in order to remain registered with the RAN, a WCD assigned the re-registration value of twenty minutes during the day may send a re-registration request to the RAN within the allotted twenty minute interval in order to ensure continued wireless service from the RAN.
Once the WCD is registered with the RAN, the WCD can then place and receive voice calls (assuming the WCD's service profile and configuration allow it). To place a call, for instance, the WCD may send a call origination message over the air (in the air interface access channel) to the RAN, providing a set of dialed digits indicative of a called party phone number. Upon receipt of the call origination message, the MSC may then direct the BSC to assign an air interface traffic channel for use by the WCD, and the MSC may further engage in call setup signaling to set up the call with a remote switch serving the called party. When the called party answers, the MSC may then connect the call through to the WCD.
On the other hand, when the MSC receives a request to connect an incoming voice call or data connection to the WCD, the MSC may page and alert the WCD over the air (in the air interface paging channel). The WCD may acknowledge the page by sending a page response to the RAN (e.g., responsive to a user pressing the “talk” button). The page response message may take various forms. After receiving the page response message, the MSC may then connect the voice call or data connection through to the WCD.
There are typically several paging channels available for a RAN to use in alerting WCDs operating in its service area of incoming voice or data connections. While several paging channels are typically available, the total number of paging channels over which a RAN (in particular, a BTS) may transmit paging messages to WCDs operating within its service area is normally set to a hard limit based on the amount of resources implemented by an owner of the RAN. For example, each BTS may have available up to seven paging channels over which to send page messages to served WCDs.
Each available paging channel may be divided into a number of timeslots during which a base station can transmit a page message to a WCD. In order to conserve battery power, each WCD is then typically arranged to operate at a given “slot cycle index” (SCI), which defines the frequency or period at which the WCD will wake up and check the paging channel for any outstanding pages. For instance, under CDMA2000, a WCD operating at a slot cycle index of 0 (zero) would wake up and check for a page every 1.28 seconds, whereas a WCD operating at slot cycle index 2 would wake up and check for a page every 5.12 seconds.
In light of the foregoing, there is an upper limit of paging channel traffic supported by the RAN. Because each transmission on the paging channel from the BTS to a WCD operating within the service area of the RAN must be assigned a particular timeslot on one of a limited number of paging channels, it is possible that the number of pending messages to be sent across the paging channels becomes greater than the number of available time slots available over the paging channels. In such a situation, pending page messages may become substantially delayed or even dropped. To a user of a WCD in the service area of the RAN and who is unaware of paging channel capacity issues, the substantial delay and/or dropping of page messages may cause user dissatisfaction with network performance and may cause device responsiveness to suffer.